Hoist



Dec. 3, 1963 e. BOULSOVER 3,112,576

HOIST Filed June 15, 1960 2 Sheets-Sheet 2 .Znyezznszar G .fioulsoer United States Patent 3,112,676 HGIST Geoffrey Boulsover, London, England, assignor to The Amalgamated Dental ompany Limited, London, England Filed June 13, 196%, Ser. No. 35,581 Claims priority, application Great Britain June 16, 1959 3 Claims. ((31. 91- 3) This invention relates to supports for the body which are adjustable in height and furnished with ram mechanism for efiecting the vertical movement, such supports being referred to as body hoists. The most usual examples are dental chairs (which term will be understood to include dental stools) and operating tables.

To stabilise the position of the support it has been found necessary to use hydraulic rams, since pneumatic rams are unduly resilient. This has meant that in, for example, operating theatres and dentists surgeries, a separate pump has been needed for the hydraulic fluid, generally being arranged for a pedal or electrical drive. An object of the invention is to avoid the need for a separate pump in the case of installations such as those just mentioned, where compressed air is usually already available. Another object is to provide for particularly smooth operation of the lifting mechanism, whilst a third object is to provide for a hydraulic ram in a body hoist of the Idnd referred to, having a minimum of moving parts, of low cost and simple construction.

The invention consists in a body hoist incorporating a closed-circuit hydraulic cylinder and plunger constrained to extend and retract as part of the hoist lifting mechanism, a supply and exhaust connection for air under pressure to operate said mechanism, and control valves for the air and hydraulic circuit coupled to direct movement of the oil to and from said cylinder in accordance with the setting of the air valve.

It will be understood that the expression closed circuit means that the hydraulic liquid is contained in the cylinder and associated liquid circuitry tubing and, unlike the compressed air, is not fed from an external source.

In one arrangement the pressurised air is arranged to operate a pneumatic lifting ram, and the hydraulic cylinder and plunger take the form of a dashpot. The hydraulic liquid is thus pressurised through the lifting mechanism rather than supplying the motivating thrust. In another arrangement, the hydraulic cylinder and plunger represent a hydraulic ram for operating the lifting mechanism, and the compressed air is led to an air space above the hydraulic liquid to pressurise the same.

Thus, the body hoist may in this second arrangement incorporate a hydraulic ram, a reservoir for hydraulic fluid with a supply and return connection to the ram and with a compressed air inlet and outlet for pressurised space above the hydraulic fluid, operator-controlled first valve means for regulating the air pressure in the reservoir, and second, hydraulic valve means for isolating hydraulic fluid in the ram from the reservoir at any desired elevation of the hoist.

In one simple construction there is a common control member for the first and second valve means arranged so that the latter is closed when the control member is in a neutral position. Movement of the control member in one direction may then open the air outlet and the return connection, whilst movement in the other direction opens the air inlet and the supply connection. To avoid spurious movement at the commencement of operation of the valves, for example if a downward movement is required but the reservoir pressure is initially high enough for an upward movement, the supply and return connections may be separately valved for oneway operation,

3,l 12$ Patented Dec. 3, 1963 "ice or the hydraulic fluid movement may be relatively restricted so that the required air pressure change is attained before any significant movement of the ram takes place. In the case of the latter alternative, a common supply and return connection without one-way valves may be employed, whilst in the former case, there may be a common connecting pipe with one-way valve means arranged for reversal by movement of the control member from one side to the other side of the neutral position.

Yet another way of avoiding spurious movement when the control member is actuated to initiate a downward movement is to provide an auxiliary hydraulic fluid chamher to which the hydraulic fluid is led from the ram, and from which it can reach the reservoir by way of a non-return valve. When the member is actuated as aforesaid the hydraulic fluid can enter the auxiliary chamber freely despite the existence of a substantial back pressure in the reservoir; the auxiliary chamber is shielded from this back pressure by the non-return valve. As the hoist descends, pressure is built up in the auxiliary chamber as a result of the accumulation of hydraulic fluid therein, but at the same time, air is being released from the reservoir. If the valve is held for sufficiently long in a position for downward movement, the pressure in the reservoir will fall below that generated in the auxiliary chamber and, generally, to atmospheric, when the hydraulic fluid in the auxiliary chamber will automatically be discharged into the reservoir.

It has been found advantageous to employ a hollow base portion of the hoist as hydraulic fluid reservoir. The ram may be mounted directly on this base, in which event a fixed hollow piston portion of the ram may represent a part of the upper air space of the reservoir, and may have the hydraulic fluid connection housed therein. Alternatively the hollow piston portion may be used as the auxiliary hydraulic fluid chamber described above.

It will be understood that the second, hydraulic valve means may be coupled to the first, air valve means by remote control; thus, in one example, the second valve means is housed within the hydraulic reservoir and is remote controlled (suitably pneumatically) to open or close a common return and supply hydraulic fluid connection for the ram according to an external control member for the first valve is displaced from, or is in, a neutral position. In this way the hydraulic fluid connecting pipes can remain within the ram, Without requiring pressure seals for an operating member.

The invention is described further with reference to the accompanying drawings, of which:

FIGURE 1 is a sectional side elevation of a platformlifting mechanism showing a control member in schematic form, not to scale, and

FIGURE 2 is a diagrammatic illustration of a hydraulic dashpot and pneumatic ram arrangement.

Referring to FIGURE 1, it will be seen that the hoist comprises a lazy tongs mechanism 1, suitably mounted on roller bearings 2, and operated by a hydraulic motor including hydraulic ram cylinder 3, pivotally attached at 4 to a lazy tongs mechanism. The ram cylinder has sliding therein a hydraulic piston 5, the interior 6 of the hydraulic cylinder being connected by a s ngle connection 1G6, 161 to the interior ill of piston 5 through valve means 9; the piston interior 19 is separated from the reservoir i1 1 by a fixed partition 12, but a connecting passage is provided by means of a pipe 13 dipping below the surface of the hydraulic fluid 14 with a non-return valve 17 incorporated in its end to prevent hydraulic fluid being forced from the reservoir into the interior 10 of the piston, which may be designated as an auxiliary chamber. The hydraulic fluid is also connected through a pipe 1%, a valve 7 and a one-way valve 8 to the pipe a.

Compressed air may be admitted to the reservoir air space by way of the compressed air pipe 21, pipe 102 and the valve means 16, and air may be exhausted from the reservoir air space by way of pipe Hi2, valve means 18 and exhaust pipe 22. 'In the arrangement shown, the control member is designed so that the valve means 9 is operated by the same means as is valve means 16, both being controlled by the operator by means of a cam driven by a suitable handle (not shown). If the cam is turned from the neutral position (shown) so that valve means 7 and 16 are opened, compressed air is admitted to the reservoir 11 through the pipe 31 and hydraulic fluid under pressure is admitted to the hydraulic cylinder 6 by way of pipe 163 and 16% and 1%, thrusting the ram cylinder 3 upwards. The area of surface in chamber 15 being greater than the area'of the piston 5, any desired mechanical advantage may be provided. The one-way valve 8 prevents any initial back surge of hydraulic fluid if the air pressure in the reservoir 11 is momentarily less than the fluid pressure in the hydraulic cylinder; such a back surge would give rise to a spurious downward movement of the ram.

When the cam 20 is turned so that valve means 9 and :18 are opened, hydraulic fluid will enter the interior 16 of the piston 5 via pipe 19%), valve 9 and pipe 101. The interior \1(} acts as the auxiliary hydraulic fluid chamber, whether or not there is a substantial back pressure in the reservoir 11, eliminating any spurious upwards movement of the ram cylinder. As the ram 3 descends, pressure is built up in the piston interior 16 as a result of the accumulation of hydraulic fluid therein, and air is exhausted to the atmosphere from the reservoir 11 via pipe 102 and valve 18 to pipe 22 so that the pressure therein will fall below that generated in the piston interior, and, generally, to atmospheric, so the hydraulic fluid in the piston interior 10 will automatically be discharged into the reservoir 11 through pipe ass. in this way the ram may be lowered until it is 'locked by turning the cam 29 into the neutral position.

As shown, the lazy tongs mechanism 1 supports a plat form 23 which may constitute the base of for example a dental chair or operating table. To avoid lateral displacement of this platform during the operation of the mechanism, slotted housings 24 are provided for each of the roller bearings 2, while a stay 25 is pivoted between platform 23 and the lazy tongs mechanism 1.

In the arrangement of FIGURE 2 the lazy tongs mechanism 1 is operated by a pneumatic ram 26 furnished with a compressed air supply '28 and return connection 2@ to an air valve 27. A hydraulic cylinder 30 and plunger 31 are connected across mechanism 1 the cylinder being closed and being connected at each end by respective pipes 37 and 38 to an oil reservoir 3-2 by way of a valve 33 to serve as a dashpot. The valves 27 and 33 are coupled by any convenient means (not shown) so that valve 33 opens when valve 27 is operated. The two may be fitted with a common operating means as in the case of FIGURE 1. In operation, when valve 27 is operated to connect pipe 36 with the compressed air supply line 28,

to extend the ram 25, valve 33 is simultaneously operated to close lines 37 and 3 8, connecting the cylinder 30 with the dashpot 32. Accordingly, the plunger 31 is allowed to retract smoothly under the control of the dashp'ot as the ram 26 extends. When valve 27 is operated to connect pipe 36 to exhaust (line 29) the simultaneous closure of valve 33 looks the hydraulic cylinder and plunger 30/31 and hence the lazy tongs mechanism 1 is locked. A similar sequence follows in the reverse sense when the ram 26 is to be retracted.

I claim:

1. A hoist actuating hydraulic motor comprising a cylinder having an open and a closed end, a hollow piston slidably engaged in the open end of said cylinder and extending therebeyond, the space between said piston and said cylinder constituting a variable volume pressure chamber, two chambers within said piston, one said chamber constituting a reservoir for hydraulic fluid and the other said chamber constituting an auxiliary chamber, hydraulic fluid in said variable volume pressure chamber and in said reservoir for hydraulic fluid, two slide valves mounted so as to be biased to closed position, means to selectively open one or other said valve, each valve having two valved passages therethrough to open and close simultaneously, one adapted to permit passage of air, the other to permit passage of hydraulic fluid, a bifurcated tubular passage means for hydraulic fluid connecting said variable volume pressure chamber to the passage for hydraulic fluid in each said valve to permit passage of hydraulic fluid, a bifurcated tubular passage means for air under pressure connecting said reservoir for hydraulic fluid to the air passage in each said valve for air under pressure, an air vent passage to atmosphere connected to the passage for air through the first of said valves, a tubular passage means for hydraulic liquid connecting said auxiliary chamber to the passage for hydraulic fluid in the said first of said valves, and a tubular passage means for hydraulic liquid connecting said reservoir below the level of said hydraulic liquid therein to the passage for hydraulic fluid in the second of said valves, a connection to the air passage of the second of said valves from a source of air under pressure, and a passage connecting said auxiliary chamber to said reservoir.

2. The hydraulic motor of claim 1, in which said passage means for hydraulic liquid connecting said reservoir to said second valve includes a check valve arranged to prevent passage of liquid toward said reservoir.

3. The hydraulic motor of claim 1, in which said passage connecting said auxiliary chamber and said reservoir includes a check valve arranged to prevent flow of liquid toward said auxiliary chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,638,075 Towler May 12, 1953 2,734,519 Widdowson Feb. 14, 1956 2,945,551 Annin et a1 July 19, 1960 3,025,837 Beach Mar. 20, 1962 

1. A HOIST ACTUATING HYDRAULIC MOTOR COMPRISING A CYLINDER HAVING AN OPEN AND A CLOSED END, A HOLLOW PISTON SLIDABLY ENGAGED IN THE OPEN END OF SAID CYLINDER AND EXTENDING THEREBEYOND, THE SPACE BETWEEN SAID PISTON AND SAID CYLINDER CONSTITUTING A VARIABLE VOLUME PRESSURE CHAMBER, TWO CHAMBERS WITHIN SAID PISTON, ONE SAID CHAMBER CONSTITUTING A RESERVOIR FOR HYDRAULIC FLUID AND THE OTHER SAID CHAMBER CONSTITUTING AN AUXILIARY CHAMBER, HYDRAULIC FLUID IN SAID VARIABLE VOLUME PRESSURE CHAMBER AND IN SAID RESERVOIR FOR HYDRAULIC FLUID, TWO SLIDE VALVES MOUNTED SO AS TO BE BIASED TO CLOSED POSITION, MEANS TO SELECTIVELY OPEN ONE OR OTHER SAID VALVE, EACH VALVE HAVING TWO VALVED PASSAGES THERETHROUGH TO OPEN AND CLOSE SIMULTANEOUSLY, ONE ADAPTED TO PERMIT PASSAGE OF AIR, THE OTHER TO PERMIT PASSAGE OF HYDRAULIC FLUID, A BIFURCATED TUBULAR PASSAGE MEANS FOR HYDRAULIC FLUID CONNECTING SAID VARIABLE VOLUME PRESSURE CHAMBER TO THE PASSAGE FOR HYDRAULIC FLUID IN EACH SAID VALVE TO PERMIT PASSAGE OF HYDRAULIC FLUID, A BIFURCATED TUBULAR PASSAGE MEANS FOR AIR UNDER PRESSURE CONNECTING SAID RESERVOIR FOR HYDRAULIC FLUID TO THE AIR PASSAGE IN EACH SAID VALVE FOR AIR UNDER PRESSURE, AN AIR VENT PASSAGE TO ATMOSPHERE CONNECTED TO THE PASSAGE FOR AIR THROUGH THE FIRST OF SAID VALVES, A TUBULAR PASSAGE MEANS FOR HYDRAULIC LIQUID CONNECTING SAID AUXILIARY CHAMBER TO THE PASSAGE FOR HYDRAULIC FLUID IN THE SAID FIRST OF SAID VALVES, AND A TUBULAR PASSAGE MEANS FOR HYDRAULIC LIQUID CONNECTING SAID RESERVOIR BELOW THE LEVEL OF SAID HYDRAULIC LIQUID HEREIN TO THE PASSAGE FOR HYDRAULIC FLUID IN THE SECOND OF SAID VALVES, A CONNECTION TO THE AIR PASSAGE OF THE SECOND OF SAID VALVES FROM A SOURCE OF AIR UNDER PRESSURE, AND A PASSAGE CONNECTING SAID AUXILIARY CHAMBER TO SAID RESERVOIR. 